1. Field of the Invention
The invention relates to the field of transmit and/or receive antennas, and more particularly to the radiating devices (or elements) of such antennas.
2. Description of the Prior Art
In the present context the term “radiating device” means a combination comprising at least a main feed line, a radiating ground plane and a resonant structure for radiating energy at a selected wavelength λ when it is excited by the main feed line, where applicable via coupling means forming part of the radiating ground plane.
The term “antenna” means not only conventional antennas such as focal array antennas, for example FAFR or passive multibeam reflector antennas, but also direct radiating active array antennas.
As the person skilled in the art knows, radiating devices or elements are usually fed by electromagnetically coupling the resonant structure to the feed line, which is parallel to the radiating ground plane and implemented in a planar technology. The feed line may be of the microstrip, coplanar or triplate type, for example, and may be coupled to the resonant structure either by proximity coupling or by electromagnetic coupling via a coupling slot formed in the radiating ground plane.
This planar technology gives rise to a certain number of technical problems.
The feed circuit being placed on or under the radiating ground plane, the resonant structure may be adversely affected by unwanted radiation or stray coupling.
The feed circuit being placed parallel to the ground plane, it is difficult to insert active equipments into the mesh of the array, such as low noise-amplifiers (LNA) or high-power amplifiers (HPA) and/or phase-shifter cells, whose dimensions are typically around 0.6λ. This problem is accentuated if the array operates with orthogonal polarizations, because it is then necessary to duplicate certain equipments (in particular certain active equipments). It is therefore insertion constraints that impose the minimum mesh sizes of the arrays. In other words, the planar technology is an obstacle to the compactness of certain array antennas.
An alternative feed is proposed in the IST Multikara 30 GHz focal array antenna project, and uses a microstrip to access guide transition followed by widening of the access guide to constitute a horn. This kind of transition cannot be used if compactness is a decisive criterion. Furthermore, it rules out dual polarization in the radiating ground plane.
Another alternative feed is proposed in the paper by K. W. Leung and M. W. To entitled “Aperture-coupled dielectric resonator antenna with a perpendicular feed”, Electronic Letters, June 1997, vol. 33, No. 12, pages 1000-1001, and feeds a dielectric resonator placed on a radiating ground plane with a microstrip line placed on another ground plane perpendicular to the radiating ground plane and having an electrical field that is “buried”, i.e. between the line and the perpendicular ground plane. This kind of solution has definite advantages in terms of isolation of the dielectric resonator and the room available for implanting equipments, but offers only a limited number of degrees of freedom, thereby making it difficult to obtain simultaneously a wide bandwidth and good quality of radiation.
No radiating device (or element) known in the art providing an entirely satisfactory solution, the invention therefore has the object of improving on the situation.